The goal of this research is to measure fingertip forces by using a multi-camera system to image coloration changes in the fingernail and surrounding skin. Key advantages of this transduction method are that objects do not have to be instrumented with force sensors, and relatively unconstrained grasps can be measured. The first four specific aims develop the measurement technique, the fifth aim is to demonstrate the measurement technique in a variety of generalized grasping scenarios. 1. Each fingernail in a multi-fingered grasp will be imaged by a high-resolution 2D camera, mounted either in a fixed position or to the back of the hand via an exoskeleton-type hand master for portability. 2. A 3D model of each fingernail surface will be developed using a stereo camera system. The 2D images from each fingernail camera will be registered to the 3D surface model using fiducial markings. 3. A magnetically levitated haptic interface will apply controlled forces and torques to the fmgerpad for calibration purposes. Data on the dependence of fingernail coloration on seven variables -- normal force, shear forces and torque, orientation of the fingerpad on a flat surface, and DIP joint angle - will be obtained. 4. The best fingernail regions and their response zones will be identified using correlation analysis, and a generalized least squares estimator of fingerpad force on the seven variables will be developed. 5. Finger force distribution for varied contact locations and finger force patterns in regrasping of objects will be characterized. Development of this imaging method will significantly expand the scope of research into the control of human grasping, and could be used clinically to characterize hand function after disease or injury. [unreadable] [unreadable] [unreadable] [unreadable]